1. Field of the Invention
This invention relates to an electronic controlled fuel injection system provided to an engine for models.
2. Description of Related Art
Heretofore, in glow engines of two-cycle or four-cycle which have been known as the engine for models, a carburetor 100 having the structure as shown in FIG. 6 as the means for controlling the feeding rate of fuel to a combustion chamber of an engine has been used.
In the housing 101 of the carburetor 100, a valve body 102 having the shape like a cylinder is provided rotatably around the axis line of the valve body 102 itself. A pipe conduit 101a and 101b extends vertically through the housing 101, and air is supplied from the upper pipe conduit 101a. A passage 102a extends through the valve body 102, and the passage is communicated to the pipe conduits 101a and 101b of the housing 101 with the opening dependent on the rotation angle of the valve body 102. An operating arm 103 is connected to a portion of the valve body 102 which projects beyond the one end of the housing 101. An operating part of a servo mechanism not shown in the drawing is connected to the operation arm 103, and the servo mechanism rotates the valve body 102 in the housing 101. A needle 104 is fixed to the valve body 102 with a screw, and the projection into the valve body 102 is adjustable by turning the needle 104.
A fuel control needle valve 105 is built-in at the other end of the housing 101. The needle valve 105 has a tube 106 and a needle 107 provided in the tube 106. The needle 107 is fixed to the tube 106 with a screw, and the needle 107 is moved inversely in the tube 106 by turning a knob 108 provided at the base of the needle, and the tip opening of the tube 106 can be adjusted. The tip of the needle 104 provided to the valve body 102 is facing to the opening of the tip of the tube 106 of the needle valve 105.
Fuel fed to the needle valve 105 is jetted from the clearance between the tip of the tube 106 and the needle 107 to the internal, mixed with air supplied in the valve body 102, and fed to an engine. Because the flow rate of fuel can be adjusted by turning the know of the needle valve 107, the flow rate of fuel (or air-fuel ratio) can be previously set so that the engine rotates at the maximum rotation speed. The servo mechanism rotates the valve body 102 to adjust air flow rate into the valve body 102, and controls the flow rate of fuel fed to the engine.
According to the carburetor 100, when the engine is accelerated rapidly from the low rotation condition such as idling, a lot of air is fed in the valve body, but the supply of fuel can not follow the supply of air, and the balance of air-fuel ratio is unbalanced. The rotation of the engine increases not smoothly and increases slowly, and can be stopped in the bad case. As a whole, the response is not good, the transition from the low rotation speed to high rotation speed or the high rotation speed to low rotation speed requires a long time, it is a disadvantage of the conventional engines. Further, in the case that an engine for models is mounted on a radio control model plane, fuel is fed not adequately to the carburetor due to the adverse effect of centrifugal force caused by flying motion of the model plane, the inadequate feeding of fuel causes the malfunction of the engine.
Inventors of the present invention had invented a novel fuel injection system to be applied to engines for models in order to solve the above-mentioned problem. The fuel injection system injects fuel into a combustion chamber of an engine for models under electronic control. The fuel injection system had been anticipated to supply fuel stably, to maintain the air-fuel ratio in balance, and to attain rapid speed response in an engine for models used in severe operational conditions.
The structure of the above-mentioned fuel injection system 30 which the inventors of the present invention had proposed is described. As shown in FIG. 5, the fuel injection system 30 is provided with an approximately cylindrical box 31. In the box 31, a solenoid coil is accommodated. A power terminal 33 for supplying power to the solenoid coil 32 is projected outside the box 31 through the box 31. A magnetic core 34 is inserted into the solenoid coil 32. A fuel supply passage 35 is formed through the axis of the magnetic core 34. The magnetic core 34 is projected outside the box beyond the base end of the box 31, and a portion of the magnetic core 34 projected outside the box 31 is communicated to the fuel supply conduit 18 guided from the fuel tank 20.
A valve box 36 is provided on the end of the box 31. A fuel injection orifice 37 is formed on the end of the valve box 36. In the box 31, an approximately cylindrical valve body 38 is inserted movably in the solenoid coil 32 adjacent to the magnetic core 34. The valve body 38 is provided with a flow passage 39 communicated to the fuel supply passage 35. A flange 40 is formed on the end of the valve body 38. A ring contact projection 41 for contact with the inside surface of the valve box 36 is provided on the periphery of the front face of the flange 40. A needle 42 is fixed at the center of the front face of the flange 40, and the needle 42 is inserted movably into the fuel injection orifice 37 of the valve body 38.
A plate spring 44 which is a pressing means for pressing the valve body 38 toward the fuel injection orifice 37 is provided between a fixing component 43 of the solenoid coil 32 and the valve box 36. The plate spring 44 comprises an outside ring fixing portion 45, inside ring moving portion 46, and connection arm 47 which connects elastically both portions. The fixing portion 45 is fixed between the fixing component 43 of the solenoid coil 32 and the valve box 36, and the moving portion 46 is fixed to the flange 40 of the valve body 38.
While power is not supplied to the solenoid coil 32, the valve body 38 is pressed toward the fuel injection orifice 37 by the pressing force of the plate spring 44, the contact projection 41 of the flange 40 is brought into contact with the inside surface of the valve body 36, and the fuel injection orifice 37 is closed. When power is supplied to the solenoid coil 32, the solenoid coil 32 attracts and moves magnetically the valve body 38 toward the magnetic core 34 against the pressing force of the plate spring 44. A space is formed between the flange 40 of the valve body 38 and the valve box 36 as the result of such movement. Fuel which is pressurized at a certain pressure in the box 31 is injected from the fuel injection orifice 37 to the outside of the box 31.
Operations of an engine for models to which the fuel injection system 30 is provided is described. Fuel injected from the fuel injection system 30 is mixed with air which is taken in depending on the opening of the throttle valve 14, and fed into a cylinder from an intake valve 17 which is opened at a predetermined timing. A glow plug 19 ignites the air-fuel mixture at a predetermined timing to start combustion. Burnt gas is exhausted outside the cylinder from an exhaust valve 23 which is opened at a predetermined timing.
However, it was found that the above-mentioned novel fuel injection system proposed by the inventors of the present invention had a problem to be solved. The fuel injection system shown in FIG. 5 supplies fuel from the rear end of the box 31 in which the solenoid coil 32 is contained into the internal thereof, the valve body 38 moves in the internal of the solenoid coil 32 filled with fuel to control fuel injection. In such structure, a failure that fuel leaks from the hole of the box 31 through which the power source terminal 33 of the solenoid coil 32 is guided to the outside can happen. Also, because the valve body 38 which receives a force from the solenoid coil is moved in fuel, the motion is slow due to resistance of the fuel, and the resistance can result in slow response speed.
It is the object of the present invention to improve the performance of the novel fuel injection system proposed by the inventors of the present invention, and to prevent leakage of fuel and to improve the response speed of the valve body by isolating the electric system from fuel.